Once, I was giving a presentation on the history of drone technology and I showed a group of high school teachers the APM 2.0, and a teacher asked me "how big of a drone could you make with that?" I didn't know how to respond at first, because really there are practical limits on the size of a drone one builds in one's basement. That's not to mention the size of recreational, RC aircraft flying in national airspace is regulated by the FAA, and also the aerospace modeling associations to which it defers some of that decision (i.e., the IMAA).
But she didn't ask me about regulations, or the capabilities of a basement UAS developer. So, I gave her the best answer I could at the time: "I'm not sure there is a limit." Because really, if you had the time, the cash, and the skills, I'm not sure there's a definable ceiling for how big you could make these DIY drones, based on the current state and availability of the technology. It's just a matter of scaling it up.
If you're like me, you've seen some pretty cool YouTube videos of large-scale RC aircraft. My favorites are the big, multi-engine replicas of propeller-driven bombers from WWII and the Cold War. Though there are some pretty cool videos of large-scale replicas of modern transports like the C-5 Galaxy, powered by small turbine engines.
Having seen those videos, I was pretty excited to learn that my local RC club would be having a large-scale fly in today. There weren't any of those multi-engine behemoths there, but I did catch a picture of this: a giant-scale J-3 Piper Cub.
Some quick specs on the beast:
J-3 Piper Cub
Twin 135cc gas motors
I'm not sure how much you could lift with this scale aircraft, but I think you could at least loft a small dog. The pilot didn't stress the "miniature" plane too much, flew it rather slow, but did show off by doing some one-wheel touch-and-gos.
I can't say that would fully support the general public making huge-scale drones that operate over people, cars, houses and that sort of thing. At least not without some kind of certification process. Having said that, this was a controlled, insured, private field, and it does make you wonder about the limits of home-built drones.
Some more pictures from the event: